Refractory regenerative furnaces



United States Patent [72] inventors Robert H. Forster [50] Field of Search 263/15, 17, Tadworth, Surrey; and 52 Leslie G.D.Sheldrake R ton-on-T ne England y y [56] References Cited [2]] Appl. No. 775,476 UNITED STATES PATENTS Filed Nov-13,1968 2,792,437 5/1957 Goinsetal 263/15X (45] Patented Nov. 10, 1970 E J h J C b [73] Assignee The British Oxygen Company Limited "mary xammer o n am y a 8mm company AttorneyTownsend & Meserole [32] Priority Nov. 20, 1967; Feb. 9, 1968 [33] Great Britain 52,716/64 and ABSTRACT: A refractory regenerative furnace comprises [52] US. Cl. 263/15 F27d-l7/00 two heat regenerative masses arranged on either side of a combustion chamber and a baffle member extending across the combustion chamber and interposed in the path of flow from one heat regenerative mass to the other, whereby a stream of gaseous material passing through the combustion chamber is constrained to flow throughan extended path.

Patented Nov. 10, 1970 3,539,162

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REFRACTORY REGENERATIVE FURNACES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to refractory regenerative furnaces for endothermically altering an endothennically alterable gaseous material.

2. Description of the Prior Art Refractory regenerative furnaces for endothermically altering endothermically alterable gaseous materials are well known. One conventional type of regenerative furnace which is widely used comprises two heat regenerative masses arranged on either side of a reaction chamber. The heat regenerative masses generally consist of a plurality of rectangular blocks of heat resisting material stacked in face to face relationship in abutting rows consisting of superimposed tiers of blocks. The opposed faces of the blocks are provided with grooves extending thereacross so that in the final assembly, grooves of adjacent faces lie in registry to define a plurality of flue passageways which extend throughthe mass.

The reaction chamber is provided with a central stack which divides the reaction chamber into two separate combustion chambers. The central stack is of similar construction to the heat regenerative masses and like each heat regenerative mass has a plurality of flue passageways extending therethrough.

In operation,the furnace is first heated by burning fuel in one of the combustion chambers in order to attain a temperature in the furnace at which the endothermic reaction will occur. Fuel is introduced into one of the combustion chambers by means of burners arranged, facing each other, on opposite sides of each combustion chamber. Air for combustion is introduced at one end of the furnace taking up heat from one of the heat regenerative masses as it proceeds towards the combustion chamber. Combustion occurs in the region of the combustion chamber after which the combustion products pass through the central stack and the other heat regenerative mass thereby imparting heat to them.

Heating is continued for a predetermined time after which the endothermic alteration is initiated by passing the endothermically alterable gaseous material through the furnace in the same direction as the combustion air and products. The gaseous material takes up heat from the first heat regenerative mass causing the endothermic alternation to occur in the region of the combustion chamber. It then passes through the central stack and the other combustion chamber and is gradually quenched as it passes through the second heat regenerative mass which is thereby heated. The endothermic alteration reaction is allowed to proceed for a predetermined interval after which the furnace is again heated, this time by .burning fuel in the other combustion chamber and feeding other is used for effecting the endothermic alteration reaction.

However, for such a process this type of furnace is subject to a number of disadvantages. In general, combustion and heat distribution throughout the furnace is poor. The combustion chambers are too small to provide for adequate mixing of the fuel with the combustion air. Mixing of the fuel and air only effectively occurs in the first combustion chamber, since mixing in the second combustion chamber is virtually prevented by the streamlining effect of the flue passageways in the central stack. Thus, unburnt gases may be swept into the flue passagewaysin the heat regenerative masses and in the central stack and an excess of free oxygen-containing air may be introduced. As a consequence, high temperature spots tend to develop in certain areas of the furnace and may lead to rapid destruction of the refractory materials of the furnace and damage to the combustion chamber burners. Temperature high spots in the furnace may also lead to carbon formation and solid deposits may be carried far into the flue passageways both in the centre stack and in the heat regenerative masses. Such deposits are difficult to remove and may lead to blockage of the flue passageways. The temperature of the exhaust gases is also liable to be excessively high and may cause expansion problems in the changeover valves which governthe periodic change of direction of gas flow through the furnace.

US. Pat. specification 2,792,437 (Goins et al.) discloses a regenerative furnace having a combustion chamber formed by a plurality of forked grooves aligned with grooves in a pair of refractory masses.

SUMMARY OF THE INVENTION The present invention aims to provide means for improving the mixing of the fuel and combustion air in the combustion chamber which thereby results in improved combustion of the fuel. The present invention effects this improvement by providing'baffle means in the combustion chamber whereby the fuel and combustion air passing through the combustion chamber is caused to traverse an extended path.

BRIEF DESCRIPTION OF THE DRAWING The present invention will now be described by way of example and with reference to the accompanying drawings in which: I

FIG. 1 is a diagrammatic plan of a horizontal section through a refractory regenerative furnace,

FIG. 2 is a diagrammatic sectional elevation through the combustion chamber of a refractory regenerative furnace,

FIG. 3 is diagrammatic perspective view of baffle means for a refractory-regenerative furnace,

FIG. 4 is a sectional elevation of a combustion chamber for a refractory regenerative furnace, 7

FIGS. 5, 6 and '7 are diagrammatic perspective views of different combustion chambers for a refractory regenerative furnace,

FIG. 8 is a sectional elevation of a combustion chamber for a refractory regenerative furnace,

FIG. 9 is a section along the line A-A of FIG. 8,

FIG. 10 is an elevation of a combustion chamber for a refractory regenerative furnace,

FIG. 11 is a section along the line 8-8 of FIG. 10 and FIG. 12 is a plan of a combustion chamber for a refractory regenerative furnace.

The furnace illustrated in FIGS. 1, 2 and 3 comprises two.

heat regenerative checkerworks l1 and 12 which are provided with straight uninterrupted flues 14 and are arranged on either side of a combustion chamber 13. Baffle means (see FIG. 3) extends transversely across the combustion chamber 13 and divides the chamber into two compartments 20 and 21.

The baffle means comprises two lateral dividing walls 24 and 25 each provided with a slot 22 and 23 respectively located at opposite sides of the furnace. A wall 26 of lesser height than the lateral dividing walls 24 and 25 is interposed in the space between these two walls.

Each compartment 20 and 21 of the combustion chamber 13 is provided with sets of burners 15 and 16 arranged in vertical rows on opposite sides of each compartment 20 and 21. Each set of burners l5 and 16 may be provided with means (not shown) by which they can be water cooled to prevent them from overheating.

The operation of the furnace in a continuous cyclic process for the thermal cracking of petroleum naphtha will now be described. The process consists essentially of a heating cycle followed by an endothermic alteration cycle in which cracking of the petroleum naphtha occurs. Heating is effected by introducing a gaseous or liquid fuel through the burner into compartment of the combustion chamber 13, igniting the burner 15 and then drawing combustion air through the checkerwork 11. The fuel is partly consumed in compartment 20 and then passes through the slot 22 in the lateral dividing wall 24, rises over the wall 26, passes into compartment 21 by way of the slot 23 in the lateral dividing wall 24 and then to exhaust through checkerwork 12. This heating cycle proceeds for 60 seconds at the end of which the flow of fuel through the burners 15 is shut off.

Steam is then drawn through the furnace for a period of 3 seconds to purge the combustion air followed by a mixture of steam and vaporised petroleum naphtha which is passed through the furnace for a further period of 57 seconds during which time the endothermic reaction takes place. The gaseous mixture of steam and petroleum naphtha flows through the checkerwork 11 into compartment 20, passes through the slot 22, rises over the wall 26, passes into compartment 21 by way of the slots 23 and flows to exhaust through checkerwork 12. At the completion of the endothermic alteration cycle the furnace reverts to the heating cycle, the direction of flow of the combustion air being reversed. Gaseous or liquid fuel is introduced through the burners 16 into compartment 21 of the combustion chamber 13, the burners 16 are ignited and combustion air drawn through the checkerwork 12. The combustion products pass through the furnace to exhaust through the checkerwork 11.

The heating cycle is then followed by the endothermic alteration cycle the direction of which is also reversed, steam and vaporised petroleum naphtha being introduced through checkerwork 12 and passing through the furnace to exhaust through the checkerwork 11. The direction of flow of the heating cycle and the endothermic alteration cycle is continuously reversed at two minute intervals to effect the cracking of petroleum naphtha.

The baffle means 30 provides a longer path of flow for the gaseous material passing through the combustion chamber 13. In addition the baffle means has the effect of imparting turbulence to the flow of the combustibles as they pass through the combustion chamber 13 thereby to provide for good mixing of the combustibles. Mixing of the combustibles is initiated in one compartment of the combustion chamber 13 and continues to completion as the gaseous material flows through the baffle means 30 and the other compartment of the combustion chamber 13.

It will be appreciated that the thorough mixing of the gaseous materials which is achieved in the combustion chamber 13 gives substantially complete combustion of the fuel and allows a uniform temperature to be attained in the furnace. As a result the life of the refractory materials of the furnace is considerably increased, since temperature high spots in the furnace are eliminated to a substantial extent and thus damage to the refractory materials caused by excessively high temperatures in the furnace avoided. Furthermore the temperature of the exhaust gases from the furnace is substantially reduced.

It will be appreciated that the construction of the combustion chamber and baffle means may take a variety of different forms. Examples of other combustion chambers and baffle means which may be employed are illustrated in FIGS. 5-12 of the accompanying drawings. These combustion chambers are all located between two heat regenerative checkerworks 11 and 12 and provided with a turret 19, mounted on the checkerworks 11 and 12, and baffle means which divides the combustion chamber into two compartments 20 and 21. In each combustion chamber the construction of the baffle means has been varied to provide different flow paths for the gaseous materialpassing through the furnace.

In the combustion chamber illustrated in FIG. 4 the baffle means comprises a lateral dividing wall 40 the top of which consists of a checkerwork portion 41 having a plurality of flue passageways 42.

In operation the gaseous material passing through the checkerwork 11 into compartment 20 is constrained by the solid base portion of the lateral dividing wall 40 to rise in the compartment 20 and pass into the compartment 21 by way of the flue passageways 42 in the checkerwork portion 41 of the lateral dividing wall 40. The walls of the turret 43 cause the gaseous material to pass down the compartment 21 and then to exhaust by way of the checkerwork 12.

It will be appreciated that the construction of the lateral dividing wall 40 provides an extended path of flow for the combustibles flowing through the combustion chamber 13 and, in addition, imparts turbulence to the flow of the combustibles thereby to provide thorough mixing thereof.

In the combustion chamber illustrated in FIG. 5 the baffle means comprises two lateral dividing walls 54 and 55, extending transversely across the combustion chamber and dividing the chamber into two compartments 20 and 21. Each wall 54 and 55 is provided with a stepped portion, constituting slots 52 and 53 respectively, located at opposite sides of the furnace, and a wall 56 is interposed in the space between the lateral dividing walls 54 and 55 so as to form a bridge between the walls at the points where the walls are stepped.

Each compartment 20 and 21 of the combustion chamber is provided with sets of burners for firing the combustibles as they pass through the combustion chamber. The burners may be arranged to fire vertically downwards as at 57a and 58a or to fire horizontally in line with the furnace axis as at 57b or to fire at right angles to the axis as at 57c. Corresponding sets of burners are similarly positioned in compartment 21.

In operation combustion air emerging from the checkerwork 11 rises to meet the fuel gas introduced into compartment 20 of the combustion chamber by way of the burners 57a, 57b or 57c. The combustion gases rise over the stepped portion of the wall 55, pass through the slot 53, and dip under the centre wall 56, whereupon they rise over the stepped portion of the wall 54, pass through the slot 52 and enter compartment 21 of the combustion chamber, passing through the furnace to exhaust by way of the checkerwork 12.

When the cycle is reversed combustion air emerges from the checkerwork l2 and is fired in compartment 21 of the combustion chamber by way of the burners 58.

In the combustion chamber illustrated in FIG. 6 the baffle means comprises a lateral dividing wall 60 the upper part of which is provided with three mixing chambers 65 consisting essentially of cylindrical slots extending through the wall 60. Two sets of burners 67 and 68 are located in the walls 63 and 64 of the turret 19 so as to fire on the air flowing through the combustion chamber and direct it through the mixing chamber 65. I i

In operation the air passes through the checkerwork 11 into compartment 20 and is constrained by the solid base portion of the lateral dividing wall 60 to rise into the turret 19 where it is fired upon the burners 57 and so directed through the mixing chambers 65 into compartment 21. On meeting the wall 64 of the turret 19 the combustibles dip in a downwards direction and flow to exhaust by way of the checkerwork 12.

In the combustion chamber illustrated in FIG. 7 the baffle means comprises a lateral dividing wall 70 which is stepped at opposite ends to provide two chambers 77 and 78 communicating between compartments 20 and 21 of the combustion chamber. Burners 75 and 76 are provided in the turret 19, the burner 75 being located in the wall 73 and directed so as to fire into the chamber 78, while the burner 76 is located in the wall 79 and directed so to fire into the chamber 77. Thus, combustion air emerging from the checkerwork 11 is con strained by the wall 70 to fiow upwards towards the chamber 78 where it is fired upon the burner 75 and caused to flow in an anticlockwise direction around the turret 19 towards the chamber 77 where it is fired upon by the burner 76 and thereby caused to flow through the chamber 77 into compartment 21 of the combustion chamber. A major portion of the combustibles dip in a downwards direction to flow to exhaust by way of the checkerwork 12, while a minor proportion of the combustibles is directed by the burner 75 into chamber 78 and recirculated around the turret 19.

it will be appreciated that it is not necessary to employ both the burners 7S and 76 to effect anticlockwise circulation of the combustibles around the turret 19. Anticlockwise circulation may be achieved using only burner 75 but a more rapid circulation is achieved when both burners 75 and 76 are employed.

1n the combustion chamber illustrated in FIGS. 8 and 9 the baffle means comprises a pair of lateral dividing walls 80 and 81, each having a solid base portion and an upper portion comprising a series of angled slots, indicated generally at 83, which communicate with each other and provide a path through which gaseous material passing through the combustion chamber may flow. The upper portion of each wall comprises a series of angled blocks 82 superimposed upon each other to provide the intcrcommunicating angled slots 83 (sec FIG. 5). Sets of burners 85 and 86 are arranged to fire into compartment 20 and 2| respectively of the combustion chamber.

in operation combustibles entering compartment 20 of the combustion chamber are constrained by the base portion of the lateral dividing wall 80 to rise upwards into the turret 19 whereupon they pass through the angled slots 83 into compartment 21 of the combustion chamber.

in the combustion chamber illustrated in FIGS. and 11 the baffle means comprises two lateral dividing walls 94 and 95 each provided with a slot 92 and 93 respectively, located at opposite sides of the furnace. A wall 96 is interposed in the space between the two walls 94 and 95 so as to provide two chambers 90 and 91 in the space between them. The upper portion of each lateral dividing wall 94 and 95 comprises a pair of checkerworks 104 and 105, and 106 and 107, respectively, each provided with a plurality of flue passageways and mounted on either side of the wall 96. Horizontal walls 88 and 89 extend across the compartments 21 and 20 respectively so as to provide separate mixing chambers 97 and 98 in the turret 19. Each compartment 20 and 21 of the combustion chamber is provided with sets of burners (not shown) arranged in vertical rows on opposite sides of each compartment.

in operation the combustibles entering the combustion chamber pass through the slot 93 and are constrained by the wall 94 to rise upwards through the chamber 91 whereupon they divide into two streams and flow through the checkerworks 104 and 105 into compartments 97 and 98 respectively. Each of these streams flow horizontally across the combustion chamber and then flow through the checkerworks 106 and 107 into the chamber 90 and travel in a downwards direction whereupon they flow through the slot 92 into compartment 20 and thence to exhaust by way of the checkerwork 11.

In the combustion chamber illustrated in FIG. 12 the baffle means comprises two dividing walls 114 and 115 and a bridging wall 116 of lesser height than the dividing walls 114 and 115. The baffle means is located diagonally across the combustion chamber thereby to divide the chamber into two compartments 20 and 21. Sets of burners 125 and 126 are arranged to tire on compartments 20 and 21 respectively.

In operation combustibles entering compartment 20 of the combustion chamber are constrained to rise over the bridging wall 116 into compartment 21 whereupon they flow to exhaust by way ofcheckerwork 12.

The refractory regenerative furnace of this invention may refinery liquefied petroleum gases petroleum naphtha, kerosene, light and heavy gas Oils, and heavier hydrocarbons.

Such materials are not limited to hydrocarbons but may include any gaseous or vaporous material, or mixtures of materials which may be endothermically altered.

We claim:

1. A refractory regenerative furnace comprising:

a. two heat regenerative masses each having a plurality of flue passageways extending therethrough;

b. a combustion chamber located between the heat regenerative masses, whereby gaseous material first passes through the flue passageways of one heat regenerative mass into the combustion chamber and then through the flue passageways of the other regenerative mass; and

c. baffle means located in the combustion chamber in the path of flow from one heat regenerative mass to the other and comprising a pair of walls and a bridging wall, the pair of walls extending transversely across the combustion chamber and each being provided with a slot for the passage of gaseous material therethrough, and the bridging wall being interposed in the flow path from.the slot in one transverse wall to the slot in the'other transverse wall, whereby a stream of gaseous material passing through the combustion chamber flows through the slot in one transverse wall, is vertically displaced by the bridging wall and then flows through the slot in the other transverse wall.

2. A refractory regenerative furnace as claimed in claim 1 in which a plurality of burners are arranged on opposite sides of the combustion chamber and positioned so as to impart turbulence to the gaseous material passing therethrough.

3. A refractory regenerative furnace comprising:

a. two heat regenerative masses each having a plurality of flue passageways extending therethrough;

b. a combustion chamber located between the heat regenerative masses, whereby gaseous material first passes through the flue passageways of one heat regenerative mass into the combustion chamber and then through the flue passageways of the other regenerative mass;

0. a turret located above the combustion chamber and out of the direct path of flow from one heat regenerative mass to the other; and v d. baffle means located in the combustion chamber and interposed in the path of flow from one heat regenerative mass to the other and comprising a wall extending transversely across the combustion chamber and into the turret, the part of the wall in the turret comprising a plurality of flue passageways extending through the wall whereby gaseous material passing from one heat regenerative mass is vertically displaced and is then constrained to flow through said flue passageways into the other heat regenerative mass. 

